Stabilisation and biological nitrogen removal (BNR) of anaerobically digested sewage sludge were studied in a post-aeration reactor at pilot scale working under alternating anoxic-aerobic conditions. Digested sludge came from a two-stage anaerobic digestion (thermophilic + mesophilic). The best post-aerator performance was achieved when working at an HRT of 10 days (4 days aerobic; dissolved oxygen of 1.8 mg L-1) and VS content in the feed no lower than 6.7 g L-1. Free ammonia concentration values in the effluent above 1.5 mg N L-1 (around 150 mg NH4 (+)-N L-1 at pH 7) were necessary to promote the BNR over nitrite. Removal efficiencies up to 80 % NH4 (+)-N, 50-55 % total nitrogen and 15-20 % VS were recorded in this study, with no external addition of chemicals. A nitrogen mass balance revealed that the high percent of NH4 (+)-N assimilated in heterotrophic growth was counteracted with that released in ammonification and fermentation, leading to a NH4 (+)-N removal mainly related to biological nitritation/denitritation.

The literature shows a diversity of real-time algorithms for automatic detection of bending-points in batch-operated waste treatment systems. In this study a new methodology is proposed for tuning the parameters of these algorithms when uncertainty specifications are considered at the outset. In this method the effects of slow and fast dynamic responses on the shape of signal trajectories were treated separately in order to cover via simulation all possible operating scenarios for a real situation. Long-term uncertainty and steady-state simulations were combined to derive probability distributions for biomasses. These probability distributions were then merged with short-term uncertainty to run one-cycle random simulations with which to reproduce the entire diversity of signal trajectories. Finally, an optimisation problem was formulated in terms of the algorithm parameters. The methodology was satisfactorily applied to tune an algorithm for detection of bending-points in an Autothermal Thermophilic Aerobic Digestion (ATAD) process. (C) 2015 Elsevier Ltd. All rights reserved.

The concept of one-stage reactor system for biological nitrogen removal over nitrite of ammonium high loaded sidestreams is going to be applied to remove nitrogen from anaerobically digested sewage sludge and to achieve its complete stabilisation. Dealing with sludge, the organic matter needed to denitrify is present in the inflow as particulate substrate, which requires a hydrolysis step. The latter implies high anoxic hydraulic retention time (HRT). During both aerobic and anoxic phases, ammonium is released which implies the need to enlarge aerobic HRT. Both effects lead to a total HRT higher than those for nitrification-denitrification of wastewater with soluble substrate. The purpose of this paper is to define, by computer simulation, a set of theoretical criteria, which will be applied later to the operation of a pilot-scale post-aeration reactor to be located in a Spanish WWTP. These criteria will be defined by simulating the reactor performance under different operating conditions. As a conclusion, some operation guidelines have been established for the above-mentioned scenario in terms of aerobic and anoxic retention time, dissolved oxygen concentration and effluent requirements (NH4 (+), NO2 (-) and NO3 (-)).